Question

How did endosymbiosis happen?

Answer 1

Endosymbiosis is a theory that defines the origin of the mitochondria and chloroplast. It is also a concept that clarifies how eukaryotic cells came to be. A close association between two separate species is called symbiosis.

Complete answer:
In eukaryotic cell evolution, endosymbiosis is a primary force. Studies of algal growth have shown that endosymbiosis has occurred many times and a number of eukaryotic cells have been developed. There are two kinds of transmissions of symbionts. Each new generation acquires free living symbionts from the atmosphere by horizontal transmission. When the symbiont is directly passed from parent to offspring, vertical transmission takes place. There is also a transition in these kinds, where symbionts are moved for some generation vertically until a host switch occurs and new symbionts are acquired from the environment horizontally. Symbionts also have a decreased genome in vertical transmissions, and are no longer able to live on their own. The symbiont relies on the host, resulting in a codependent relationship that is highly intimate. For important molecules, pea aphid symbionts have lost genes and now depend on the host to supply nutrients to them. The symbionts for the aphid host synthesize essential amino acids. Several instances of endosymbiosis are mandatory; that is, without the other, either the endosymbiont or the host will not survive, such as the gutless marine worms of the genus Riftia, which are nourished by their endosymbiotic bacteria.

Note:
Examples of endosymbiosis best studied are known from invertebrates. These symbioses affect species with a worldwide impact, including coral symbiodinium or insect wolbachia. Most insect farming pests and vectors of human disease have intimate experiences with primary endosymbionts.